This application is related to and claims priority from Japanese Patent Application No. 2002-192201 filed on Jul. 1, 2002, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vapor compression refrigerant cycle for transferring heat from a low-temperature side to a high-temperature side. More particularly, the present invention relates to a rotational speed control of a compressor in the vapor compression refrigerant cycle at an operation starting time of the compressor. The vapor compression refrigerant cycle is suitably used for an air conditioner.
2. Description of Related Art
For example, in JP-B-2902061, a capacity of a vapor compression refrigerant cycle is controlled by controlling a rotational speed of a compressor to a target value that is determined based on a set temperature, a room air temperature and an outside air temperature. In this vapor compression refrigerant cycle, when a fixed throttle having a fixed open degree is used as a decompression device, the following problem is caused. For example, if the room air temperature and the outside air temperature are high, an air-conditioning load of the vapor compression refrigerant cycle (air conditioner), that is, a cooling load thereof is large, so a large cooling capacity is required. Therefore, a control unit for controlling the compressor sets a target rotational speed of the compressor at a high value, and controls the compressor by the set target rotational speed.
Accordingly, in a case where the cooling load of the air conditioner is large such as in the summer, when the compressor of the air conditioner is operated, the target rotational speed is set at the high value. Further, at this time, refrigerant pressure in the vapor compression refrigerant cycle has already increased before an operation start of the compressor. As a result, refrigerant pressure at a high pressure side in the vapor compression refrigerant cycle may exceed its allowable pressure. Furthermore, if the fixed throttle is adopted as the decompression device, the refrigerant pressure at the high pressure side increases approximately in proportional to the square of the rotational speed of the compressor. As a result, the refrigerant pressure at the high pressure side may exceed the allowable pressure when the operation of the compressor is started. If the refrigerant pressure at the high pressure side exceeds the allowable pressure, a safety device of the compressor operates. Therefore, the operation of the compressor is stopped, and the operation of the vapor compression refrigerant cycle for the air conditioner is stopped.
In view of the above-described problems, it is an object of the present invention to provide a vapor compression refrigerant cycle capable of preventing pressure abnormality from being generated when operation of a compressor is started in a large cooling load.
According to an aspect of the present invention, a vapor compression refrigerant cycle includes a compressor for compressing and discharging refrigerant, a high-pressure heat exchanger for radiating heat of high-pressure refrigerant discharged from the compressor, a decompression device that decompresses the high-pressure refrigerant from the high-pressure heat exchanger, a low-pressure heat exchanger for evaporating low-pressure refrigerant after being decompressed in the decompression device, and a control unit for controlling a rotational speed of the compressor. In the vapor compression refrigerant cycle, the control unit sets a starting target rotational speed of the compressor at an operation starting time of the compressor based on a refrigerant pressure of the compressor at the operation starting time such that the starting target rotational speed is reduced as the refrigerant pressure increases, and the control unit starts the compressor by the starting target rotational speed. Accordingly, when the operation of the compressor is started, pressure of the high-pressure refrigerant can be prevented from exceeding an allowable pressure in the vapor compression refrigerant cycle. Therefore, when the operation of the compressor is started in a high load state, it can prevent a pressure abnormality from being generated in the refrigerant cycle.
Alternatively, the control unit sets the starting target rotational speed of the compressor based on at least one of an air temperature around the high-pressure heat exchanger and an air temperature around the low-pressure heat exchanger such that the starting target rotational speed is reduced as at least one of the air temperatures increases, and the control unit starts operation of the compressor by the starting target rotational speed. Generally, as the air temperatures become higher, the refrigerant pressure at the operation starting time of the compressor is increased. Accordingly, by reducing the starting target rotational speed as at least one of the air temperatures increases, it can prevent the pressure abnormality from being generated in the refrigerant cycle.
Further, in the present invention, as the decompression device, an ejector including a nozzle or a variable throttle can be used.
According to another aspect of the present invention, the control unit calculates a starting target rotational speed of the compressor at the operation starting time of the compressor based on one of the refrigerant pressure in the compressor, an air temperature in a compartment and an air temperature around the high-pressure heat exchanger such that the starting target rotational speed is reduced as the one of the refrigerant pressure and the air temperatures increases. Further, the control unit calculates a general target rotational speed based on a target temperature of air to be blown into the compartment. In addition, the control unit has determining means that determines a smaller one among the starting target rotational speed and the general target rotational speed, as a determined target rotational speed at the operation starting time. In this case, the control unit starts operation of the compressor by the determined target rotational speed. Accordingly, it can effectively prevent the pressure abnormality from being generated in the refrigerant cycle.